Stagnant Atmosphere Research Articles

Modeling of the Calm Situations in the Atmosphere of Almaty

This article addresses modeling of the atmospheric boundary layer of the city of Almaty (Kazakhstan) in stagnant, environmentally unfavorable conditions using WRF Model. The city is located on the northern slope of Trans-Ili Alatau, where the rate of recurrence of calm and low-wind (1–2 m/sec) days reaches about 80%. All simulations were made for a period from 28.11.2016 to 05.12.2016, covering main synoptic situations of the stagnant atmosphere: the extent of Asian anticyclone, higher and lower pressure gradient fields. The model integrated three nested domains with grid sizes 9, 3 and 1 km, respectively. The initial boundary conditions were formed based on ERA5-reanalysis. Subject to the WRF model requirements, the land-use map with a standard USGS set (24 categories) was developed, to which 3 categories of the urban areas were added. The most relevant configuration of parameterization methods was selected: short-wave and long-wave radiation (Mlawer), surface layer (Monin-Obukhov similarity theory), urban area (BEP), boundary layer (Bougeault-Lacarrere), turbulence (Smagorinsky). The article demonstrates that the WRF model adequately reflects fundamental urban atmosphere patterns in the most unfavorable anticyclone periods of the autumn-winter season. It was established that the accuracy of estimates decreases with the transition to weak cyclonic activity. Based on the simulation results and remote sensing data, the territory in question is divided into four climatic zones to which a comparative method was applied; however for a detailed correlative analysis a denser network of meteorological stations is required. Calculations showed that the wind along the Ili river valley prevails in the northern part, regularly changing its western direction to eastern. Near the mountain area mountain-valley wind circulation prevails. The blocking inversion layer has a strong impact. The urban heat islands strongly depend on wind conditions. For example, a nocturnal heat island is cooled by the cold wind flow from the mountains.

The influence of atmospheric blocking on regional PM10 aerosol transport to South Korea during February–March of 2019

The particulate matter (PM10) trend has decreased at a growing rate in South Korea, which is on the downwind side in the East Asian region over the last five-year period of 2014–2018. Nevertheless, nationwide, days of high PM10 levels and haze frequently occurred over the period of February–March in 2019. During the period of February–March 2019, two major atmospheric blockings were identified over the Alaskan region in the northeast Pacific over the periods of February 21-March 1 and March 18–29. Warm and stagnant synoptic meteorological conditions favorable for high-PM10 haze days in the East Asian region were accompanied 4–5 days later by the remote Alaskan atmospheric blockings. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) was used, applying zero-out emission to analyze the regional PM10 contribution on severe haze days exceeding a daily average of 100 μg m−3 over South Korea during March 3–6, 2019. The daily average regional PM10 contribution indicated a rate of 57% compared to rates of 23% before and 29% after severe haze days. Furthermore, the major regional PM10 components were nitrates (49%), other inorganics (28%), and sulphates (9%) during the severe haze days. Among inorganic PM10 aerosols, other inorganics mainly composed of anthropogenic fine dust were not a major contribution component in the South Korean case due to fuel consumption changes in China. However, higher nitrate flux from sources in eastern China remained in South Korea, though in slightly reduced amounts. The contribution rate of NOX discharged from automobiles has gradually increased in China, and the level of SO2 remained on a low level through emission control technologies and regulatory options. The warm and stagnant atmosphere in the East Asian region caused the flux of relatively more nitrates were likely transported, with ammonium nitrate in the atmosphere and with lower sulphate levels.

Viscoacoustic squeeze-film force on a rigid disk undergoing small axial oscillations

This paper investigates the air flow induced by a rigid circular disk or piston vibrating harmonically along its axis of symmetry in the immediate vicinity of a parallel surface. Previous attempts to characterize these so-called ‘squeeze-film’ systems largely relied on simplifications afforded by neglecting either fluid acceleration or viscous forces inside the thin enclosed gas layer. The present viscoacoustic analysis employs the asymptotic limit of small vibration amplitudes to investigate the flow by systematic reduction of the Navier–Stokes equations in two distinct flow regions, namely, the inner gaseous film where streamlines are nearly parallel to the confining walls and the near-edge region of non-slender flow that features gas exchange with the surrounding stagnant atmosphere. The flow in the gaseous film depends on the relevant Stokes number, defined as the ratio of the characteristic viscous time across the film to the characteristic oscillation time, and on a compressibility parameter, defined as the square of the ratio of the acoustic time for radial pressure equilibration to the oscillation time. A Strouhal number based on the local residence time emerges as an additional governing parameter for the near-edge region, which is incompressible at leading order. The method of matched asymptotic expansions is used to describe the solution in both regions, across which the time-averaged pressure exhibits comparable variations that give opposing contributions to the resulting time-averaged force experienced by the disk or piston. A diagram structured with the Stokes number and compressibility parameter as coordinates reveals that this steady squeeze-film force, typically repulsive for small values of the Stokes number, alternates to attraction across a critical separation contour in the parametric domain that exists for all Strouhal numbers. This analysis provides, for the first time, a unifying viscoacoustic theory of axisymmetric squeeze films, which yields a reduced parametric description for the time-averaged repulsion/attraction force that is potentially useful in applications including non-contact fluid bearings and robot locomotion.

On the mechanism of single pellet smouldering combustion

Aiming at improving the design of wood pellet stoves and boilers, we developed original experiments to study chemical and physical processes occurring in a single pellet. We investigated medium temperature (<550 °C) and low air flowrate, where smouldering prevails. Two setups have been used, allowing to monitor the pellet weight loss, internal temperature, and the exhaust gas composition (H2, CO, CO2, O2, VOC), and modify the temperature and composition of the environment surrounding the pellet and its size. The study allowed to identify the sequence of phases involving drying, pyrolysis, partial and total oxidation of volatiles and char. The maximum rate of conversion is controlled by heat conduction, in the gas surrounding the solids and within the porous pellet, thus, it is linearly proportional to the environment temperature. At the higher temperature, the char yield decreases, and the useful heat must be extracted from volatiles combustion (in the gas phase) rather that embers (char combustion). An axial smouldering front, from the fractured edges prevails over a radial one, from the side of the pellet, due to a less permeable layer left by the extrusion process. Experiments in a nearly stagnant atmosphere clarified that both volatiles and char oxidations occur under O2 starvation; the rate is proportional to O2 available. Also, evidence of a transition from 1- to 2-films char combustion are identified, suggesting that O2 mass transfer controls the heterogeneous char oxidation first, and then the CO oxidation in the gas phase, at higher surface temperature.

Entrance length effects on the flow features of rectangular liquid jets

An experimental study was carried out to investigate the effects of entrance length on the main characteristics of rectangular liquid jets discharged into the stagnant atmosphere. Six rectangular nozzles, all with the same aspect ratio of 3 but with different entrance length ratios ranging from 3.3 to 60 were constructed. The physics of the fluid flows was visualized by the aid of backlight shadowgraph technique and high speed photography. Flow visualizations revealed that in the mid-range of Weber numbers, the perturbations induced over the liquid surface remarkably depended on the entrance length ratio. Moreover, the characteristics of the axis-switching instability of rectangular liquid jets were measured. It was found that axis-switching wavelength was independent of the entrance length, while the amplitude of axis-switching was directly influenced. For entrance length ratios smaller than 10, the amplitude was increased with increase of entrance length, whereas for entrance length ratios higher than 10, this trend was reversed. Measurements of breakup length also showed that the transition of flow regimes was not perceptibly affected by the entrance length.

Impact of control measures and typhoon weather on characteristics and formation of PM2.5 during the 2016 G20 summit in China

The implementation of strict emission control during the G20 summit in China and the occurrence of Typhoon Malarkas in September 2016 provided a valuable opportunity to examine the role of control measures and special weather condition in the formation of PM2.5. Water-soluble inorganic ions (WSII) were measured hourly in addition to PM2.5 mass concentration and black carbon (BC) and gaseous pollutants in Ningbo located in the Yangtze River Delta (YRD) region of China. Three distinct cases, i.e., a control case, a normal case, and a typhoon case, were investigated during the study period. PM2.5 was higher in the control case (37.5 μg m−3) than in the normal case (29.8 μg m−3), whereas the lowest PM2.5 (14.2 μg m−3) was observed in the typhoon case. The analyses of meteorology and backward trajectory suggested that stable weather and regional transport from inland regions accounted for the high PM2.5 under strict control. Only the concentrations of Ca2+ and NO3− decreased in the control case, while those of all water-soluble inorganic components (except Na+ and Mg2+) decreased substantially in the typhoon case. SO42− dominated the WSII, with the highest contribution, 62%, in the control case. This result was attributed to a stagnant atmosphere with a high relative humidity (RH), which was beneficial for the transformation of SO2 to SO42−. The control and typhoon cases both resulted in extremely low NO2, but the contribution of NO3− to PM2.5 was reduced in the control case and increased in the typhoon case. The close correlation of the NOR (nitrate oxidation ratio) with Na+ and Mg2+ in the typhoon case was indicative of sea salt associated with the typhoon which provided a surface for the heterogeneous formation of NO3−. The presented results facilitate a better understanding of the characteristics and formation of PM2.5 under the influence of artificial control and natural intervention.

Vertical profiles of particle light extinction coefficient in the lower troposphere in Shanghai in winter based on tethered airship measurements

A cavity attenuated phase shift single scattering albedo monitor was set up on a tethered airship platform to study the vertical profiles of particle light extinction coefficient (bext) in the lower troposphere (<1000 m) in Shanghai during 12–29 December 2015. Clear transition heights (THs) for vertical profiles of bext during the polluted days (PM2.5 > 75 μg m−3) were observed below 1000 m. The vertical differences of bext were highly dynamic as the vertical variation in bext was significant by as much as 605 Mm−1. The TH was observed mostly at about 100–200 m, and 450–650 m during night and daytime, respectively, and was in a wide range of ∼50–900 m during 15:00–22:00 due to the low boundary layer and/or the transport of pollutants. In particular, the TH was consistently below 500 m throughout the day during highly polluted haze episodes, highlighting the important role of a stagnant atmosphere situation for high concentrations of PM2.5. The vertical distribution of bext did not have a constant rule with respect to relative humidity and wind. Sometimes, peak values of bext at ∼350 m and 500 m during daytime were caused by enhanced regional transport. During stagnant and highly polluted situations or well-mixed clean days, bext was usually uniformly distributed below and above the TH, respectively, although bext was much smaller above the TH. For other situations, local emissions, pollutant transport, and the physical and chemical characteristics of aerosols resulted in highly dynamic vertical profiles of bext.

Fireworks: A major source of inorganic and organic aerosols during Christmas and New Year in Mexico city

Abstract The fireworks activity in Christmas and New Year is the culprit of a substantial increase in the particles pollution during those festivity dates in Mexico City. The fireworks' thrilling explosions fill the air with small particles full of metals and organic and inorganic species, and noxious gases such as sulfur dioxide, nitrogen dioxide, carbon monoxide and nitrous acid (HONO). The stagnant atmosphere at night accumulates the fireworks haze under a shallow boundary layer. By sunrise, once the fireworks activity has stopped, the photolysis of the abundant HONO accumulated throughout the night, leads to a rapid production of nitrate (NO3−), ammonium (NH4+), sulfate (SO42−) and low volatility secondary organic aerosols. This was the pattern observed during the winter of 2013–2014, when online measurements of water-soluble inorganic ions in particles smaller than 2.5 μm (PM2.5), non-refractory ions and organics in particles smaller than 1 μm (PM1), equivalent black carbon, and above-mentioned gases were conducted. The geometric average of the sum of the three major inorganic ions, NO3−, NH4+ and SO42− accounted for 25% (28%) and 34% (37%) of the total PM2.5 mass during the fireworks activity at night and the following morning on Christmas Day (New Year's Day), respectively. Similarly, their sum in the non-refractory fraction accounted for 37% (49%) and 47% (53%) of the total NR-PM1 mass concentration, while the organic fraction accounted for 56% (44%) and 49% (44%). Biomass burning organic aerosols and semi-volatile oxygenated organic aerosols (BBOA and SV-OOA, respectively) dominated the organic fraction during the fireworks period at night, while the low-volatility oxygenated organic aerosols (LV-OOA) increased substantially their concentration along the post-firework hours the following morning. Concentrations of PM2.5 > 100 μg m−3 and PM1 > 50 μg m−3 were observed on both days, with maximums of 157 and 137 μg m−3 for PM2.5 and PM1, respectively. The meteorological conditions helped to reduce the fireworks impact by late afternoon on both days, limiting the firework episodes to 22 h. The SO42− and NO3− related to the fireworks were not able to offset the deficit of NH4+, and thus the acidity nature of the particles during the mild winter of Mexico City did not change.

Characteristics and Concentration of White Dust and The Particulate Matter (PM10) in Erdenet city, Mongolia

The purpose of this research was to determine characteristics and composition of white dust in the tailings pond of Erdenet Copper Mining (ECM) and to identify mass concentration of the particulate matter (PM10) around Erdenet city. Based on these goals, we determined critical level of flaring speed for white dust and how to reduce this speed. Meteorological data and particulate matter (PM10) were collected from the Research Institute of Meteorology, Hydrology and Environment (IRIMHE) and Air Quality Monitoring Station (AQMS) in Erdenet city. The mass concentration of par-ticulate matter (PM10) were analyzed and compared with WHO guidelines and Mongolian air quality standard (MNS4585:2016). Critical speed of flaring was tested in the laboratory condition and based on that we had estimated total number of days that white dust released into the air. In addi-tion, in order to reduce flaring white dust, watering method was tested in the laboratory and based on that the moisture amount to avoid flaring of white dusts had estimated. Results were shown that spring and autumn have a significantly higher level of mass concentration of PM10 in Erdenet city. It was caused by the stagnant atmosphere which leads to pollution’s cumulative effect and white dust from the storage of tailings pond during spring and autumn. Particle size of white dust had two types, 2-0.05 mm sandy and 0.05-0.002 mm dusty; yet it had a high concentration of As, Pb, Zn and Cu that were higher than the Mongolian national standard of heavy metals for soil. The critical level of flaring speed was about 4-5 m/s. Based on this critical level of flaring speed for white dust, on average 25 days per month had flaring white dust. The test result in the laboratory was shown that 5 percent of moisture would reduce the flaring

Corrosion behavior of Hastelloy® C–4® Ni–Cr–Mo–Fe alloys for coal gasification syngas plants

Abstract A mechanistic exposure experiment was performed on welded samples of the commercially available Haynes® Hastelloy® C–4® Ni-Cr-Mo-Fe alloy (65 wt.-% Ni, 16 wt.-% Cr, 16 wt.-% Mo, 3 wt.-% Fe, 2 wt.-% Co, 1 wt.-% Mn, 0.7 wt.-% Ti, 0.5 wt.-% Cu, 0.08 wt.-% Si and 0.01 wt.-% C) at coal gasification pilot plant facilities affiliated with the Institute for Advanced Engineering in Yongin-si, South Korea. The alloy samples were preoxidized at 400 °C under a stagnant air atmosphere for 24 h prior to exposure to the corrosive environment (60 % CO, 28.4 % H2, 2.5 % CO2, 0.8 % CH4, 600 ppm H2S and 110 ppm carbonyl sulfide under 2.005 MPa pressure and 170 °C). Thermodynamic Ellingham-Pourbaix stability diagrams were constructed to provide insight into the mechanism of the observed corrosion behavior prevailing in the piping materials between the particulate removal unit and water scrubber of the coal gasification pilot plant. The thermodynamic inference of the corrosion mechanism was supplemented with morpholo...

WHITE DUST SIMULATION FOR TAILINGS POND OF ERDENET COPPER MINING USING HYSPLIT

The purpose of this research was to identify dispersion and transporting of white dust for tailings pond of Erdenet copper mining in Mongolia. Spring and autumn have a significantly higher level of PM10 mass concentration in Erdenet city. Probably caused by the stagnant atmosphere which leads to pollution’s cumulative effect and ‘white dust’ from the storage of tailings pond in spring and autumn. We used meteorological data for 2015 gathered from Information and Research Institute of Meteorology, Hydrology and Environment (IRIMHE) in Erdenet city and GDAS meteorological data provided by U.S NOAA. In the present study, white dust simulation by using the ArcGIS, HYSPLIT program modeling. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is used to identify the white dust dispersion and transportation trends. According to the simulation from model HYSPLIT, white dust was spread between 14 and 65 km in 2015. The main month of white dust distribution was May and October when mass concentration of PM10 was high due to white dust. White dust distribution was four times lower when the rainy day.

Aerodynamics of axisymmetric counterflowing jets

The laminar flow resulting from impingement of two steadily fed low-Mach-number gaseous jets issuing into a stagnant atmosphere from coaxial cylindrical ducts at moderately large Reynolds numbers, often used in combustion experiments, is studied through numerical integrations of the Navier–Stokes equations. In the Reynolds-number range addressed, 50–1000, the flow of the approaching jets is nearly inviscid, with viscous effects and mixing being restricted to the thin mixing layers surrounding the jets and to a thin layer located at the separating stream surface. The analysis of the main inviscid flow shows that only two parameters, based on the scales associated with the radius and the velocity profiles of the two feed streams, are needed to characterize the flow, namely, the ratio of the inter-jet separation distance to the duct radius and the ratio of momentum fluxes of the jets. The numerical results for uniform and Poiseuille velocity profiles provide, in particular, the value of the strain rate at the stagnation point for use in the analysis of experimental studies of counterflow premixed and diffusion flames.

Electrochemical characterization of Fe-air rechargeable oxide battery in planar solid oxide cell stacks

Abstract Iron-air rechargeable oxide batteries (ROB) comprising solid oxide cells (SOC) as energy converters and Fe/metal-oxide redox couples were characterized using planar SOC stacks. The charge and discharge of the battery correspond to the operations in the electrolysis and fuel cell modes, respectively, but with a stagnant atmosphere consisting of hydrogen and steam. A novel method was employed to establish the stagnant atmosphere for battery testing during normal SOC operation without complicated modification to the test bench and stack/battery concept. Manipulation of the gas compositions during battery operation was not necessary, but the influence of the leakage current from the testing system had to be considered. Batteries incorporating Fe2O3/8YSZ, Fe2O3/CaO and Fe2O3/ZrO2 storage materials were characterized at 800 °C. A maximum charge capacity of 30.4 Ah per layer (with an 80 cm2 active cell area) with ∼0.5 mol Fe was reached with a current of 12 A. The charge capacity lost 11% after ∼130 ROB cycles due to the increased agglomeration of active materials and formation of a dense oxide layer on the surface. The round trip efficiencies of the tested batteries were ≤84% due to the large internal resistance. With state-of-the-art cells, the round trip efficiency can be further improved.

Characteristics of PM1.0, PM2.5, and PM10, and Their Relation to Black Carbon in Wuhan, Central China

Hourly average monitoring data for mass concentrations of PM1, PM2.5, PM10, and black carbon (BC) were measured in Wuhan from December 2013 to December 2014, which has a flourishing steel industry, to analyze the characteristics of PM and their relation to BC, using statistical methods. The results indicate that variations in the monthly average mass concentrations of PM have similar concave parabolic shapes, with the highest values occurring in January and the lowest values appearing in August or September. The correlation coefficient of the linear regression model between PM1 and PM2.5 is quite high, reaching 0.99. Furthermore, the proportion of PM1 contained within PM2.5 is roughly 90%, directly proving that ultrafine particles whose diameter less than 1 μm may be a primary component of PM2.5 in Wuhan. Additionally, better seasonal correlation between PM and BC occurs only in summer and autumn, due to multiple factors such as topography, temperature, and the atmosphere in winter and spring. Finally, analysis of the diurnal variation of PM and BC demonstrates that the traffic emissions during rush hour, exogenous pollutants, and the shallow PBLH with stagnant atmosphere, all contribute to the severe pollution of Wuhan in winter.

Enhancement of Oxygen Transport in the Storage Electrode of a High Temperature Secondary Metal-Air Battery Based on an Oxygen Ion Conducting Electrolyte

The concept of a new reversible metal air battery with high cycling capability is based on a porous structure of iron-iron oxide serving as storage of low oxygen activity which is coupled to the negative electrode of a solid oxide fuel / electrolyzer cell via gas diffusion in stagnant atmosphere of a gaseous redox couple. The positive electrode is supplied by air. Such concept does not suffer from the problem of degrading contacts in the storage electrodes caused by volume change of solid phases upon charge and discharge. Basic quantitative reasoning shows that as gaseous redox couple a mixture of hydrogen and water vapor is ideally suited to achieve high performance. Experimental results are presented, which demonstrate the low overall polarization of this kind of storage concept.

Study of experimental and theoretical procedures when using thermogravimetric analysis to determine kinetic parameters of carbon black oxidation

Combustion of carbon black (CB) in the crucible of a thermobalance is controlled by both carbon reactivity and oxygen transport from the oxidizing flux to the surface of the bed and within the porous bed. The kinetic constant of combustion has been determined using a fixed-bed reactor in which CB combustion is mainly under kinetic control. Then, modelling of oxygen transport in the thermobalance allowed determining the oxygen diffusivity within the CB pile. Fickian diffusion is a good approximate value of the diffusion coefficient for modelling of internal oxygen transport. The effects of the initial sample mass and of the sample containment on the initial combustion rate have been investigated. The effectiveness factor of the bed was calculated for different experimental conditions. Advices to correctly extract a kinetic constant from thermogravimetric experiments are given. According to the required precision, an experimental procedure is proposed. Limitations to oxygen transport within the bed may be ignored. They can be minimized by the use of an inert material to remove the stagnant atmosphere between the surface of the bed and the mouth of the crucible. It appears mandatory to account for oxygen transport limitations within the CB pile. It can be assumed that the sample temperature (not known) during reaction is the regulation temperature. Thermal effects are also minimized by use of the inert material. A 30–50 mg sample mass seems to be optimal for determination of the kinetic parameters.

Introduction

Introduction

Mathematical treatment of the discharge of a laminar hot gas in a stagnant colder atmosphere

We study the boundary-layer approximation of the classical mathematical model that describes the discharge of a laminar hot gas in a stagnant colder atmosphere of the same gas. We prove the existence and uniqueness of solutions to a nondegenerate problem (without zones of stagnation of gas temperature or velocity). The asymptotic behavior of these solutions is also studied

Theory of vaporization of a rigid spherical droplet in slowly varying rectilinear flow at low Reynolds numbers

The vaporization of a droplet in rectilinear motion relative to a stagnant gaseous atmosphere is addressed for the limit of low Reynolds numbers and slow variation of the droplet velocity. Approximations are introduced that enable a formal asymptotic analysis to be performed with a minimum of complexity. It is shown that, under the conditions addressed, there is an inner region in the vicinity of the droplet within which the flow is nearly quasi-steady except during short periods of time when the acceleration changes abruptly, and there is a fully time-dependent outer region in which departures of velocities and temperatures from those of the ambient medium are small. Matched asymptotic expansions, followed by a Green's function analysis of the outer region enable expressions to be obtained for the velocity and temperature fields and for the droplet drag and vaporization rate. The results are applied to problems in which the droplet experiences constant acceleration, constant deceleration and oscillatory motion. The results, which identify dependences on the Prandtl number and the transfer number, are intended to be compared with experimental measurements on droplet behaviours in time-varying flows.

Springtime soluble particles in a suburban area of Taichung in central Taiwan

Continuous measurements of concentrations of soluble species between fine and coarse particles were made using a RP 2300 sampler to characterize springtime particulate pollutants in Shalu, a suburban area of Taichung, Taiwan. Particulate matter was closely observed from March 4 to April 2, 2006. The characteristics of ambient particulates were investigated during the winter monsoon period, the weak winter monsoon period and the non-winter monsoon period. The wind speed influenced the ratio of the mass concentration of coarse particles to that of fine particles. The ratio was high during the strong winter monsoon because the coarse particles were re-suspended by high wind speed. In contrast, the low ratio was associated with the accumulation of local anthropogenic particles in a stagnant atmosphere in the non-winter monsoon period. The increases in the concentrations of soluble SO 4 2− and NO 3 − species were associated with the long-range transport of pollutants from the Asian Continent and local urban pollution emissions, respectively. Factor analysis was performed on the measurements to determine the variances of the identified sources among the three atmospheric conditions. The deviations from the seawater Cl −/Na + ratio of 1.16 in the coarse particles indicated the notable deficit of chloride. A large amount of air pollutants was transported by airflow during a dust event: the mass concentrations of fine particles and coarse particles in a dust event were 30% and 160% higher than those in a non-dust event, respectively.